Cell Growth and Division

1
Cell Growth and Division

• Biology Chapter 8
• Pg. 158-171

2
Limits of Cell Growth

• Why do cells divide?
• Larger cells would have difficulty getting
  getting O2 and nutrients into the cell and waste
  products out of the cell
• Not enough RNA could be made to support the needs
  of the growing cell.
• Growth is the addition of cells not each cell
  getting bigger

3
Rates of Cell Growth

• What determines how fast cells divide?
• This is determined by the nature of the cell
  itself.
• bacteria cells take approx. 30 min.
• other single celled organisms take approx.
• 1 hr.
• skin cells take approx. 10 hours

4
Rates of Cell Growth

• How many cells are produced by the human body
  each day?
• Approx. 2 trillion cells daily- this is about
  25 million cells per second!!
• Every second approx 2 million red blood cells are
  produced.

5
Rates of Cell Growth

• If bacteria can divide every 30 minutes, why
  havent they taken over the world?
• They quickly use up all the available nutrients
  and the rate of growth slows down

6
Calculations

• A certain strain of bacteria divides once every
  30 minutes under ideal conditions. After 12 hours
  how many bacteria would there be?
• Answer 16,777,216

7
Controls on Cell Growth

• Cells in the skin and digestive tract go through
  mitosis throughout your life, other cells such as
  nerve and heart cells rarely divide.
• Cell division can be turned on or off during
  injury the switch must be turned on and cells
  at the edge of the injury divide rapidly, when
  the healing process is complete mitosis slows
  down.

8
Controls on Cell Growth

• If cells are not replaced when they are worn out
  or when there is an injury, what might be some of
  the consequences for the organism?
• Wounds would not heal, internal bleeding,
  non-functioning organs, and ultimately death
  would occur.
• This is why nerve damage and heart damage are
  permanent.

9
Uncontrolled Cell Growth

• What is cancer?
• Cancer is a disorder in which some cells have
  lost the ability to control their own rate of
  growth.

10
Abnormal Cell Growth

• Abnormal growth can produce a disorganized mass
  of cells called a tumor.
• Benign tumors remain in place and grow,
  interfering with function of healthy tissue.
• Malignant (cancerous) tumors are invasive and
  extend into surrounding tissue.
• Cancer is a collection of many disorders.

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Genes and Cancer

• Oncogenes activate genes that increase cell
  division.
• Tumor suppressor genes hold mitosis in check.

12
Genes and Cancer

• A mutagen is an environmental factor that causes
  a change in DNA
• A carcinogen is a mutagen that specifically
  causes cancer.

13
Chromosomes

• Chromosomes are structures that contain genetic
  information.
• Humans have 23 pairs (46) of chromosomes
• Chromosomes are tightly coiled chromatin.

14
DNA Structure

• Chromatin is composed of DNA and protein.
• DNA is coiled around proteins called histones
• DNA and histones form nucleosomes

Figure 4.19
15
The Cell Cycle

• The series of changes that a cell undergoes from
  the time it forms until it divides is called the
  cell cycle.

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The Cell Cycle

• G 1 is the first Gap or Growth phase. During this
  period, cell growth occurs.
• S phase is the period of DNA replication as the
  cell prepares for cell division.

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The Cell Cycle

• G 2 is the second Gap or Growth phase. During
  this period, the cell replicates organelles in
  preparation for cell division.

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Mitosis

• Occurs in eukaryotic cells
• Mitosis occurs in all somatic cells, (body
  cells) with the exception of sex cells.
• Cell division results in two genetically
  identical cells with 46 chromosomes each.
• Mitosis is nuclear division.
• Cytokinesis is division of the cytoplasm.

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Figure 3.37
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The Cell CycleInterphase

• Interphase is the period of cell growth and
  function.
• Interphase is composed of G1, S Phase, and G2.

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The Cell CycleInterphase

• Interphase is the period of cell growth and
  function.
• Interphase is composed of G1, S Phase, and G2.

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Mitosis (PMAT) Prophase

• 1. Chromatin condenses and forms chromosomes
• 2. Centrioles move to the poles, spindle fibers
  attach to the centromeres
• 3. Nuclear membrane and the nucleolus disappear

23
Mitosis (PMAT) Metaphase

• 1. Chromosomes align up across the equator of the
  cell.

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Mitosis (PMAT) Anaphase

• 1. Spindle fibers contract and the sister
  chromatids separate becoming individual
  chromosomes
• 2. Chromosomes move to the opposite poles.

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Mitosis (PMAT) Telophase

• 1. Chromsomes uncoil back into chromatin
• 2. Spindle fibers break apart
• 3. Nuclear membrane and the nucleolus reappear

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Cytokinesis

• As mitosis ends,
• Cytokinesis
• begins. During
• cytokinesis the
• cytoplasm and
• organelles are
• Divided equally.

• Cy

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Plant Cell Mitosis

• Plant cells do not have centrioles
• Instead of pinching apart, plant cells form a
  cell plate.

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Figure 8
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Cytoplasmic Division

• Cytokinesis begins in anaphase, it is the
  division of the cytoplasm and the organelles
• Animal cells pinch apart
• Plant cells form a cell plate

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Cellular Differentiation

• The process by which different cells develop
  different structures and specialized functions is
  called differentiation.
• Cellular differentiation begins in the first
  weeks after fertilization.
• It reflects genetic control. Special proteins
  activate some genes and repress others.

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Figure 8
32
Control of Cell Division

• How often cells divide is strictly controlled.
• Cells appear to keep track of their divisions,
  the mitotic clock.
• DNA at tips of chromosomes, telomeres, wear down
  as the cell divides and may be a signal for the
  cell to stop dividing.
• Size, space, hormones, and growth factors
  influence cell division.